Because of poor seed germination, milfoil can spread and reproduce by fragmentation. It produces fragments during the summer after fruiting once, or twice then the shoots get carried away by currents or boaters, and they form new plants.
Due to milfoil’s ability to spread rapidly and the density of a milfoil infestation, it often blocks out sunlight for plants native to the lakes. The plant can also inhibit the movement of larger fish, therefore disrupting the predator-prey relationship. Many waterways become congested, and the plant can cause serious damage to outboard motors and fishing gear due to these dense groups as well. Some lakes have even been rendered unsuitable for marine activities due to milfoil infestation!
Chemicals are frequently used to control milfoil growth. However as the milfoil dies and drops to the bottom, there is a huge oxygen demand which can cause fish kills and anoxic conditions at the bottom of the lake. This dead plant material results in more organic sediment and nutrient availability, and likely leads to either future aquatic weed growth or potentially worse, toxic cyanobacteria growth.